Two of the most common types of semiconductor die packages currently used are plastic packages and ceramic packages. Ceramic packages are preferred over plastic packages in some instances (e.g. when hemeticity and/or high frequency is required), but plastic packages are generally preferred over ceramic packages because plastic packages are less expensive.
Plastic packages are routinely used to package silicon die, however, attempts to package GaAs semiconductor die in plastic packages have proven somewhat problematic. For example, although relatively thick GaAs die (i.e. those die having a thickness greater than about 3 mils) can be packaged in plastic, power dissipation characteristics of thick GaAs die limit the maximum power capabilities that can be implemented.
In order to overcome the power dissipation problems and allow more complex circuits, attempts have been made to reduce the thickness of the GaAs die to less than 3 mils. However, the die handling processes associated with packaging are incompatible with thin, i.e. less than 3 mils, GaAs die. The use of a thick, about 18 μm, gold back metal layer has been proposed in an attempt to strengthen GaAs die thinned for power dissipation purposes. Unfortunately, the thick gold back-metal layer is incompatible with plastic packaging processes for at least two reasons: 1) the thick gold causes embrittlement of the soft-solder used in plastic packaging processes to attach the semiconductor die to the leadframe; and 2) gold tends to de-laminate from a plastic package.
What is needed, therefore, is away to allow high-powered GaAs semiconductor die to be used in plastic packages. By allowing a high-powered semiconductor die to be used in a plastic package, substantial cost savings could be achieved without performance loss.